Overburden/tailings mixtures for engineered tailings deposit control

ABSTRACT

A process for enhancing the solidification of tailings is provided comprising providing overburden having a moisture content ranging from about 15 wt % to about 25 wt % and comminuting the overburden to a first size; providing tailings having a solids content ranging from about 1 wt % to about 70 wt %; adding the tailings to the first sized overburden to form treated overburden and comminuting the treated overburden to a second size; and depositing the second sized treated overburden to produce a substantially solidified deposit.

FIELD OF THE INVENTION

The present invention relates to a process for enhancing thesolidification of tailings. In particular, tailings and overburden arecombined in a process involving overburden crushing to form a suitabledeposit for disposal and/or further environmental desiccation.

BACKGROUND OF THE INVENTION

Oil sand generally comprises water-wet sand grains held together by amatrix of viscous heavy oil or bitumen. Bitumen is a complex and viscousmixture of large or heavy hydrocarbon molecules which contain asignificant amount of sulfur, nitrogen and oxygen. The extraction ofbitumen from sand using hot water processes yields large volumes of finetailings composed of fine silts, clays, residual bitumen and water.Mineral fractions with a particle diameter less than 44 microns arereferred to as “fines.” These fines are typically clay mineralsuspensions, predominantly kaolinite and illite.

The fine tailings suspension is typically 85% water and 15% fineparticles by mass. Dewatering of fine tailings occurs very slowly. Whenfirst discharged in ponds, the very low density material is referred toas thin fine tailings. After a few years when the fine tailings havereached a solids content of about 30-35%, they are referred to as fluidfine tailings which behave as a fluid-like colloidal material. The factthat fluid fine tailings behave as a fluid and have very slowconsolidation rates significantly limits options to reclaim tailingsponds. A challenge facing the industry remains strengthening the oilsand tailings deposits so that they can be reclaimed and no longerrequire containment.

Recently, the present applicant developed a process for dewatering oilsands tailings by treating the tailings with coagulant and flocculantprior to dewatering by centrifugation (see U.S. patent application Ser.No. 13/594,402, incorporated hereto by reference). The centrifugationprocess is particularly useful with, but not limited to, fluid finetailings. Dewatering the tailings by centrifugation enables reclamationof tailings disposal areas and recovery of water for recycling. However,one challenge faced by the applicant is disposal of the resultantcentrifuge cake. Cake properties are a function of the solids contentand water chemistry. It was discovered that, while the addition ofgypsum improved the conveyability of the cake from the centrifuge,typically, the produced cake from the centrifugation process still onlyhad a solids content of about 50 to 55% by weight (about 31% by volume)and a shear strength of about 0.5 to 2.0 kPa. Thus, furtherstrengthening of the centrifuge cake is desirable.

Accordingly, there is a need for an improved method to treat finetailings to strengthen same and reduce their water content in order toreclaim the land on which fine tailings are disposed.

SUMMARY OF THE INVENTION

The current application is directed to a process for enhancing thesolidification of tailings by combining tailings and overburden in aprocess involving overburden crushing to form a suitable deposit fordisposal and/or further environmental desiccation. The present inventionis particularly useful with, but not limited to oil sands tailings suchas fluid fine tailings (FFT, formerly known as MFT—Mature FineTailings), oil sand tailings centrifuge cake, process affected water,water (aqueous) fluid wastes such as water treatment brine, oil sandtailings thickener underflow, flue gas desulfurization gypsum slurry,and the like (hereinafter collectively referred to as “oil sandstailings”). However, it is understood that the present invention can beused with any mining tailings, slurry and the like. It was surprisinglydiscovered that by conducting the process of the present invention, oneor more of the following benefits may be realized:

(1) Tailings are combined with overburden. The average lump size iscontrolled by a crushing process to yield a deposit which easilysolidifies, absorbs process-affected water, and exhibits propertiessuitable for reclamation.

(2) A deposit having a tailings:overburden mixture ratio of at least0.2:1.0 (bulk volume, i.e., the volume of the overburden after theoverburden has been excavated from the mining face) exhibits anundrained shear strength greater than 5 kPa which complies withregulatory requirements.

(3) Compaction further increases the undrained shear strength of adeposit having low tailings content and overburden having highplasticity, low moisture content, and composed of fine lumps. Thereduction in the tailings moisture content and associated increase inthe tailing solids content increases the undrained shear strength of thedeposit.

(4) Centrifuge cake obtained from the centrifugation of treated FFT andoverburden co-mixing reduces the footprint used to confine centrifugecake by about ⅛^(th) and substantially reduces the time (i.e., to almostzero) to achieve trafficable deposit mass strength of 25 kPa. Forexample, it would likely only require a deposition site havingdimensions of 450 m×800 m×40 m to contain/sequester approximately 5-6million dry tons of fines.

(5) Field tests confirm that centrifuge cake and overburden can be mixedusing pre-determined ratios and nearly 100% liquid phase absorptionoccurs within 24 hours without significantly changing the volume of thedeposit.

(6) 25-50 kPa initial mass strength deposits are achievable bycontrolling the mix ratio of overburden to cake at about 1.5 BCM (bankcubic meters, i.e., the volume prior to excavation) to about 1 m³ cake(˜75% solids concentration).

(7) A substantially solidified deposit is formed which can be reclaimedinto dry landscape in about a one year cycle.

Thus, use of the present invention enables reclamation of tailingsdisposal areas.

In one aspect, a process for enhancing the solidification of tailings isprovided, comprising:

-   -   providing overburden having a moisture content ranging from        about 15 wt % to about 25 wt % and comminuting the overburden to        a first size;    -   providing tailings having a solids content ranging from about 1        wt % to about 70 wt %; and    -   adding the tailings to the first sized overburden to form        treated overburden and comminuting the treated overburden to a        second size to produce a substantially solidified deposit.

In one embodiment, the treated overburden is further comminuted to athird size to produce the solidified deposit. In another embodiment, thetailings are oil sands tailings. In another embodiment, the oil sandstailings are fluid fine tailings (FFT). In another embodiment, the oilsands tailings are centrifuge cake.

In another aspect, a process line for enhancing the solidification oftailings is provided comprising:

-   -   a first comminution device for comminuting overburden to a first        size;    -   an overburden preparation apparatus for contacting the        overburden with incoming tailings to form treated overburden;    -   a second comminution device for comminuting the treated        overburden to a second size to produce a substantially        solidified deposit.

In one embodiment, the process line further comprises a thirdcomminution device for further comminuting the second sized treatedoverburden to a third size. In one embodiment, the comminuting devicesare sizers such as two roll crushers, four roll crushers, and the like.In one embodiment, the first comminution device comminutes theoverburden to a first size of about 600 mm. In another embodiment, thesecond comminuting device comminutes the treated overburden to a secondsize of about 200 mm. In yet another embodiment, the third comminutingdevice comminutes the second sized treated overburden to a third size ofabout 100 mm.

BRIEF DESCRIPTION OF THE DRAWINGS

Referring to the drawings wherein like reference numerals indicatesimilar parts throughout the several views, several aspects of thepresent invention are illustrated by way of example, and not by way oflimitation, in detail in the figures, wherein:

FIG. 1 is a schematic showing one embodiment of a process line inaccordance with the present invention.

FIG. 2 is a plot of the increase in undrained shear stress (KPA) of theoverburden/FFT mixture versus the weight percent of the solids in theoverburden/FFT mixture.

FIG. 3 shows a schematic of poldering which incorporates alternatinglayers of mixed overburden/FFT and sand.

FIG. 4 is a Casagrande plasticity chart plotting the liquid limitagainst the plasticity index.

FIG. 5 is an activity chart plotting the clay-sized fraction against theplasticity index.

FIG. 6 is a graph showing the peak undrained shear strength over timefor fine and coarse samples of the Kca facies.

FIG. 7 is a graph showing the peak undrained shear strength over timefor fine and coarse samples of the Kcb facies.

FIG. 8 is a graph showing the peak undrained shear strength over timefor fine and coarse samples of the Kcc facies.

FIG. 9 is a graph showing the peak undrained shear strength over timefor fine and coarse samples of the Kcw facies.

FIG. 10 is a graph showing the peak undrained shear strength over timefor fine and coarse composite mixtures.

FIG. 11 is a graph showing the peak undrained shear strength over timefor compacted fine and coarse samples of the Kca facies.

FIG. 12 is a graph showing the peak undrained shear strength over timefor compacted fine and coarse samples of the Kcb facies.

FIG. 13 is a graph showing the peak undrained shear strength over timefor compacted fine and coarse samples of the Kcc facies.

FIG. 14 is a graph showing the peak undrained shear strength over timefor compacted fine and coarse samples of the Kcw facies.

FIG. 15 is a graph showing the effect of the mixture ratio on long termundrained shear strength.

FIG. 16 is a graph showing the effect of shale lump size on long termundrained shear strength.

FIG. 17 is a graph showing the effect of the mixture ratio on suction.

FIG. 18 is a graph showing the effect of shale lump size on suction.

FIG. 19 is a graph showing the moisture content over time for facies Kcaas determined by Methods 1 and 2.

FIG. 20 is a graph showing the moisture content over time for facies Kcbas determined by Method 2.

FIG. 21 is a graph showing the moisture content over time for facies Kccas determined by Method 2.

FIG. 22 is a graph showing the moisture content over time for facies Kcwas determined by Methods 1 and 2.

FIG. 23 is a graph showing the FFT moisture content over time for Kcacoarse 0.6 as determined by Method 3.

FIG. 24 is a graph showing the FFT moisture content over time for Kcwcoarse 0.6 as determined by Method 3.

FIG. 25 is a graph showing the FFT solids content over time for Kcacoarse 0.6 as determined by Method 3.

FIG. 26 is a graph showing the FFT solids content over time for Kcwcoarse 0.6 as determined by Method 3.

FIG. 27 is a graph showing the moisture absorption over time for facieshaving coarse shale lumps.

FIG. 28 is a graph showing the moisture absorption over time for facieshaving fine shale lumps.

FIG. 29 is a graph showing the FFT solids content over time for faciesKca and Kcw at mixture ratios of 0.4 and 0.6.

FIG. 30 is a graph showing the FFT solids content over time for faciesKca, Kcb, Kcc and Kcw.

FIG. 31 is a graph showing the FFT solids content over time for faciesKca, Kcb, Kcc and Kcw.

FIG. 32 is a graph showing the effect of the mixture ratio on suctionover time for Kca-FFT mixtures.

FIG. 33 is a graph showing the effect of the mixture ratio on suctionover time for Kcb-FFT mixtures.

FIG. 34 is a graph showing the effect of the mixture ratio on suctionover time for Kcc-FFT mixtures.

FIG. 35 is a graph showing the effect of the mixture ratio on suctionover time for Kcw-FFT mixtures.

FIG. 36 is a graph showing the undrained vane shear strength over timefor Kca-FFT mixtures.

FIG. 37 is a graph showing the undrained vane shear strength over timefor Kcb-FFT mixtures.

FIG. 38 is a graph showing the undrained vane shear strength over timefor Kcc-FFT mixtures.

FIG. 39 is a graph showing the undrained vane shear strength over timefor Kcw-FFT mixtures.

FIG. 40 is a graph showing the undrained vane shear strength over timefor facies Kca, Kcb, Kcc and Kcw.

FIG. 41 is a graph showing the effect of compaction on shear strength ofKca-FFT mixtures.

FIG. 42 is a graph showing the effect of compaction on shear strength ofKcb-FFT mixtures.

FIG. 43 is a graph showing the effect of compaction on shear strength ofKcc-FFT mixtures.

FIG. 44 is a graph showing the effect of compaction on shear strength ofKcw-FFT mixtures.

FIG. 45 is a graph showing the undrained vane shear strength over timeof composite mixtures.

FIG. 46 is a graph showing the undrained vane shear strength over timeof saline water and facies Kca, Kcb, Kcc and Kcw.

FIG. 47 is a graph showing the moisture transfer of water vapour tosmall clay-shale lumps over time.

FIG. 48 is a graph showing the moisture transfer of water vapour tolarge clay-shale lumps over time.

FIG. 49 is a graph showing the solids content over time for facies Kca,Kcb, Kcc and Kcw.

FIG. 50 is a graph showing the undrained shear strength (kPa) of FFTCake (FFTC) when overburden (Kca) is added to FFTC.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The detailed description set forth below in connection with the appendeddrawings is intended as a description of various embodiments of thepresent invention and is not intended to represent the only embodimentscontemplated by the inventor. The detailed description includes specificdetails for the purpose of providing a comprehensive understanding ofthe present invention. However, it will be apparent to those skilled inthe art that the present invention may be practiced without thesespecific details.

The present invention relates generally to a process for treatingtailings derived from oil sands extraction operations and containing afines fraction. Combining tailings and overburden in a process involvingoverburden crushing forms a suitable deposit for disposal and/or furtherenvironmental desiccation. As used herein, the term “tailings” meanstailings derived from oil sands extraction operations and containing afines fraction. The term is meant to include fluid fine tailings (FFT)from tailings ponds and fine tailings from ongoing extraction operations(for example, thickener underflow or froth treatment tailings) which maybypass a tailings pond.

In one embodiment, the tailings are primarily FFT obtained from tailingsponds given the significant quantities of such material to reclaim. Thetailings stream from bitumen extraction is typically transferred to atailings pond where the tailings stream separates into an upper waterlayer, a middle FFT layer, and a bottom layer of settled solids. The FFTlayer is removed from between the water layer and solids layer via adredge or floating barge having a submersible pump. In one embodiment,the FFT has a solids content ranging from about 10 wt % to about 60 wt%. In one embodiment, the FFT has a moisture content of about 60%. TheFFT may be passed through a screen to remove any oversized materials.

In one embodiment, the screened FFT may be pumped into an agitated feedtank for combining with a suitable additive. The preferred additive maybe selected according to the tailings composition and processconditions. However, optimum additives such as, for example, coagulantsand flocculants, have been identified for the effective dewatering oftailings and production of amenable recycle water. As used herein, theterm “coagulant” refers to a reagent which neutralizes repulsiveelectrical charges surrounding particles to destabilize suspended solidsand to cause the solids to agglomerate. Suitable coagulants include, butare not limited to, gypsum, lime, alum, polyamine or any combinationthereof. As used herein, the term “flocculant” refers to a reagent whichbridges the neutralized or coagulated particles into largeragglomerates, resulting in more efficient settling. Flocculants arecharacterized by molecular weights ranging between about 1,000 kD toabout 50,000 kD, and various charge densities (i.e., anionic, nonionic,or cationic). Suitable natural polymeric flocculants may bepolysaccharides such as dextrin, starch or guar gum. Suitable syntheticpolymeric flocculants include, but are not limited to, charged oruncharged polyacrylamides, for example, a high molecular weightpolyacrylamide-sodium polyacrylate co-polymer having a medium chargedensity (about 20-35% anionicity).

Other useful polymeric flocculants can be made by the polymerization of(meth)acrylamide, N-vinyl pyrrolidone, N-vinyl formamide, N,Ndimethylacrylamide, N-vinyl acetamide, N-vinylpyridine,N-vinylimidazole, isopropyl acrylamide and polyethylene glycolmethacrylate, and one or more anionic monomer(s) such as acrylic acid,methacrylic acid, 2-acrylamido-2-methylpropane sulphonic acid (ATBS) andsalts thereof, or one or more cationic monomer(s) such asdimethylaminoethyl acrylate (ADAME), dimethylaminoethyl methacrylate(MADAME), dimethydiallylammonium chloride (DADMAC), acrylamidopropyltrimethyl ammonium chloride (APTAC) and/or methacrylamidopropyltrimethyl ammonium chloride (MAPTAC). The preferred flocculant maybe selected according to the FFT composition and process conditions.

As used herein, the term “overburden” means a layer of rocky clay-likematerial which overlies an oil sand deposit. In one embodiment, theoverburden comprises consolidated clay-shale material. In oneembodiment, the overburden has a moisture content ranging from about 15wt % to about 25 wt %. In one embodiment, the overburden has a moisturecontent of about 20 wt %.

The run of mine overburden is transported from a surface mine orstockpile, and deposited into a sizer. As used herein, the term “sizer”means a crushing apparatus capable of comminuting the overburden intogranular material and crushing oversized rock and other large lumpmaterials into a granular material. In one embodiment, the overburden isfed through rotors having teeth. As the overburden falls into thecrushing chamber, the teeth grip the overburden. The pressures createdby the narrow gap and the force of the teeth rip the overburden apartinto granular material having a reduced, more manageable lump size. Inone embodiment, the granulated overburden has an average lump size ofabout 600 mm. The granular overburden is expelled from the underside ofthe sizer and transported to a processor bed.

In one embodiment, the processor bed has a frame supporting rotatingelements and may be oriented with respect to horizontal to provide ahorizontal surface or incline. The processor bed is operable as a sizerto crush the granular overburden in a wet process. The FFT and granularoverburden are combined together by spraying the FFT onto the granularoverburden prior to entering one or more sizers. In one embodiment, theFFT-to-overburden ratio ranges from about 0.2:1.0 (bulk volume) to about0.4:1.0 (bulk volume). Preferably, the FFT-to-overburden ratio is about0.2:1.0 (bulk volume). In one embodiment, two sizers are used. The firstsizer decimates the overburden/FFT mixture from an average lump size ofabout 600 mm to about 200 mm. The second sizer decimates theoverburden/FFT mixture from an average lump size of about 200 mm toabout 100 mm. The product yielded from crushing the overburden/FFTmixture will hereinafter be referred to as the “deposit.”

Turning now to the specific embodiment shown in FIG. 1, the overburden16 is excavated using a mobile shovel 12. The shovel 12 dumps theas-mined overburden 16 into a truck 14 for transport to the firstcomminuting stage 1. In this embodiment, first comminuting devicecomprises a double roll crusher 18 (also referred to as a primarysizer). The crusher 18 comminutes the as-mined overburden to a firstsize, for example, to about 600 mm. The first sized overburden isdelivered to a surge bin 20. One or more apron feeders 22 extend intothe base of the surge bin 20 for removing the first sized overburden ata slow, controlled, sustained mass flow rate. The apron feeder 22 isupwardly inclined and transport and feed the first sized overburden tothe upper end of an overburden preparation unit 24.

Overburden preparation unit 24 comprises inlet 36 having nozzles forspraying the overburden with FFT, for example, having 35 wt % solids. Inone embodiment, the FFT has been pre-treated with a coagulant and/or aflocculant. The overburden preparation unit further comprises asecondary sizer comprising a four roll crusher 26 designed to reduce theparticle size of the overburden to approximately 200 mm (the secondsize). In this embodiment, overburden preparation unit 24 furthercomprises a tertiary sizer comprising a four roll crusher 28 designed toreduce the size of the overburden to approximately 100 mm. The blendedoverburden/FFT mixture (treated overburden) is the transported by trucks(not shown) to a deposition site. The resultant blended overburden/FFTwith have a solids content of about 70 wt % or higher.

It will be appreciated by those skilled in the art that other methodsmay be used to combine the FFT and granular overburden to yield asolidified deposit. In one embodiment, hydraulic fracturing may be used,whereby the FFT may be injected at high pressure into layers ofoverburden stored in a waste dump.

As used herein, the term “shear strength” means the magnitude of theshear strength which a material can sustain. The term “undrained shearstrength” means the shear strength of the material when pore water hasnot been drained from the material. The term “liquid limit” means themoisture content at which a material begins to behave as a liquid. Theundrained shear strength of FFT alone is low since the moisture contentis substantially higher than the liquid limit. The undrained shearstrength of FFT centrifuge cake is also fairly low, typically less than2 kPa. In contrast, the undrained shear strength of overburden is highbecause the moisture content is below the liquid limit. Theoverburden/FFT deposit exhibits an undrained shear strength greater thanthe undrained shear strength of the FFT alone. Similarly, theoverburden/centrifuge cake deposit exhibits an undrained shear strengthgreater than the undrained shear strength of centrifuge cake alone. Inone embodiment, the overburden/FFT deposit has an undrained shearstrength greater than about 5 kPa. In one embodiment, the overburden/FFTcentrifuge cake deposit has an undrained shear strength greater thanabout 25 kPa. In one embodiment, the overburden/FFT centrifuge cakedeposit has an undrained shear strength between about 25 kPa to about 50kPa.

Without being bound by any theory, the greater undrained shear strengthof the overburden/FFT deposit is attributed to the moisture transferfrom the FFT to the overburden within the mixture. The moisture transferand greater undrained shear strength thus facilitate handling anddisposal of both overburden and tailings.

In one embodiment, the overburden/FFT deposit and/or the overburden/FFTcentrifuge cake deposit has a solids content of at least about 70 wt %.In one embodiment, the overburden/FFT deposit and/or the overburden/FFTcentrifuge cake deposit has a moisture content which approaches optimummoisture content. As used herein, the term “optimum moisture content”means the percentage of moisture in a material at which the material canbe compacted to its greatest density. An overburden/FFT deposit having amoisture content close to its optimum moisture content results in ahigher undrained shear strength than that of a deposit having a moisturecontent exceeding the optimum moisture content. A deposit approachingoptimum moisture content can thus achieve an appreciable level ofcompaction. As used herein, the term “compaction” means a process inwhich stress is applied to the deposit to cause densification as air isdisplaced from the pores among the solids. In one embodiment, thedeposit may be compacted before disposal or dewatering.

FIG. 2 shows the increase in undrained shear stress (KPA) of theoverburden/FFT mixture (i.e., treated overburden) versus the weightpercent of the solids in the treated overburden. It can be seen in FIG.2 that increasing the proportion of overburden (i.e., increasing the wt% of solids) resulted in a significant increase in undrained shearstrength.

The overburden/FFT deposit may be collected and transported via aconveyor, pump or transport truck to a disposal area. At the disposalarea, the overburden/FFT deposit is stacked to maximize dewatering bynatural processes including consolidation, desiccation and freeze thawvia 1 to 2 m, or greater than 2 m thick annual lifts to deliver atrafficable surface that can be reclaimed.

In another embodiment, the overburden/FFT deposit may be placed inlayers which alternate with layers of compacted lifts. In oneembodiment, the compacted lifts comprise sand. Such a configuration oflayers not only delivers a trafficable surface but also facilitatesdrainage. In another embodiment, poldering can be used. A polder is alow-lying tract of land enclosed by embankments (barriers) known asdikes that forms an artificial hydrological entity. FIG. 3 shows aschematic of poldering which incorporates alternating layers of mixedoverburden/FFT and sand. A dike 100 is built and layers ofoverburden/FFT 150 placed in the dike with alternating layers of sand152.

Exemplary embodiments of the present invention are described in thefollowing Examples, which are set forth to aid in the understanding ofthe invention, and should not be construed to limit in any way the scopeof the invention as defined in the claims which follow thereafter.

EXAMPLE 1 Materials

The Clearwater Formation constitutes the majority of the overburden(75-85 m thick) overlying the McMurray Formation oil sands (Alberta,Canada) and is formed of several layers. The base layer, Kcw, is shallowmarine glauconite with sand interbeds and some clay shale, with anaverage clay content of 23%. High water retention is observed in the Kcwclay due to its low permeability and high porosity. The Kcw is 3-5 mthick and contains traces of bitumen. The Kca unit is 3-5 m thick, withan average clay content of 50%. With increasing depth, the compositionof the unit changes from silty clay to dark grey clay silt. The Kca ischaracterized as a weak and highly plastic unit. The Kcb unit is 4.5-6 mthick, with an average clay content of 60%, of which the majority is lowdensity smectite. The Kcc unit is 21-23 m thick. Six siltstone layersinterspersed with light grey clay silt compose the layer such that theclay content varies from 18-70%. High porosities (36-50%) result in ahigh potential for expansion and swelling. The Kce and Kcf units aretypically present in thick overburden that is not traditionally surfacemined. The Kcd unit is the uppermost unit for surface mining but is notalways encountered due to glacial scouring.

Samples of Kca, Kcb, Kcc, and Kcw were tested (i.e., four 20 L bucketsof split 3-inch core samples of Kca and Kcw facies and three 20 Lbuckets of split 3-inch core samples of Kcb and Kcc facies). Twelvebuckets of FFT and two buckets of recycled mine water (each 20 Lbuckets) were also used. Shale samples were broken manually into lumpsabout 5 mm in size and filtered through a US #4 sieve (4.75 mm). Allmaterial passing the sieve was retained and set aside, while materialretained on the sieve was re-processed until all material passed. Theprocedure was repeated using a US #10 sieve (2 mm), but care was takento ensure that half of the shale was retained on the sieve and halfpassed through the sieve. Coarse (2-4.75 mm) and fine (less than 2 mm)shale lump sizes were used. Processing was performed rapidly to maintainthe in-situ moisture content, and all processed material was sealed incontainers covered with plastic wrap.

EXAMPLE 2 Index Testing of Individual Materials

Index tests were performed to assess various properties of the shalefacies and the FFT (Tables 1 and 2). Bitumen content was not assessed,but included as part of the liquid phase.

TABLE 1 Test Shale FFT As-Received Moisture Content X X Atterberg limits(with recycled mine water) X X Atterberg Limits (with distilled water) X(tests performed on selected samples) Specific Gravity X X OrganicContent X X Particle Size Analysis (Sieve-Hydrometer) X X ConsolidationX Surface Area X Methylene Blue Index (MBI) X X-Ray Diffraction (XRD) XX Energy Dispersive X-Ray Spectroscopy X (tests performed (EDX) onselected samples) Dean Stark Testing X Bulk Density X Recycled MineWater (RCW) Testing N/A N/A

TABLE 2 Atterberg Limits ¹Samples tested with recycled mine waterMoisture ² Samples tested with Organic Content distilled water SpecificContent Sample [%] LL [%] PI [%] LI [%] Gravity [%] Kca-1 23.9 117.492.7 −0.9 2.80 3.1 Kca-1a N/A 115.0 N/A N/A N/A Kca-2 16.6 138.8 116.9 −4.5 2.82 Kca-2a N/A 130.7 N/A N/A N/A Kca-3 15.1 121.3 97.8 −8.6 2.78Kca-3a N/A 120.8 N/A N/A N/A Kcb-1 30.8 123.9 97.9 4.9 2.80 2.1 Kcb-1aN/A 120.6 95.3 N/A N/A Kcb-2 29.7 152.4 128.9  4.8 2.77 Kcb-2a N/A 117.890.1 N/A N/A Kcb-2b N/A 164.1 N/A N/A N/A Kcb-2c N/A 130.3² 106.7²  N/AN/A Kcb-3 25.0 81.5 63.8 11.4 2.74 Kcb-3a N/A 82.1 63.2 N/A N/A Kcc-121.7 60.7 41.4 5.8 2.77 2.7 Kcc-2 19.6 63.8 45.0 1.8 2.74 Kcc-3 19.178.8 60.7 1.6 2.76 Kcc-3a N/A 77.0 57.7 N/A N/A Kcw-1 13.8 64.5 47.1−7.6 2.78 2.9 Kcw-2 14.3 65.2 49.7 −2.4 2.79 Kcw-3 16.3 40.2 25.3 5.52.68 Kcw-3a N/A 50.6 34.8 N/A N/A FFT-1 132.3  70.8 48.2 227.6 2.35 14.4FFT-2 132.2  72.8 50.5 217.6 2.36 14.1i. Moisture Content

Three samples of each shale facies and two samples of the FFT weretested. Moisture content is defined as:w=m _(w) /m _(s)×100  (1)where w=moisture content; m_(w)=mass of water; and m_(s)=mass of solids.The lowest moisture content was observed in Kcw (average of 15%), withthe highest noted in Kcb (average of 29%), The average moisture contentsof Kcb, Kca, and Kcc were 29%, 19%, and 20%, respectively. The averagemoisture content of the FFT was 132%.ii. Atterberg Limits

Three samples of each shale facies and two samples of the FFT weretested for Liquid Limit (LL) and Plastic Limit (PL). The PlasticityIndex (PI) is defined as:PI=LL−PL  (2)Since initial tests on some of shale facies indicated significantvariability in the LL and the PL, subsequent tests were performed. Withthe exception of one sample, all tests were performed using recycledmine water. The test on Kcb-2c was performed using distilled water, andthe results for Kcb-2c fell within the range of plasticity valuesobserved on the recycled mine water samples (Kcb-2, Kcb-2a, Kcb-2b),indicating that distilled water does not significantly impact theplasticity of the shale facies.

Kca exhibits the highest plasticity, while Kcw has the lowest plasticity(FIGS. 4-5). In general, the shale facies and FFT are primarilyclassified as medium and high plasticity clay. The LL and PI for Kcaranged from 115-139% and 93-117%, respectively. The average LL and PI ofKca was 124% and 103%, respectively. Kcb had a LL and PI ranging from82-164% and 63-129%, respectively. Similarly, Kcc had a LL and PIvarying between 61-79% and 41-61%, respectively. The LL and PI resultsfor Kcw ranged from 40-65% and 25-50%, respectively. The average LL was124%, 120%, 70%, and 55% for Kca, Kcb, Kcc, and Kcw, respectively. Theaverage PI was 103%, 90%, 51%, and 39% for Kca, Kcb, Kcc, and Kcw,respectively.

The above results indicate a significant capacity for moistureabsorption. Kca and Kcb exhibited the highest potential for moistureabsorption, where the average moisture content ranged from 18-28%, theaverage LL varied from 120-124%, and the average Liquidity Index (LI)ranged from −5-7%. Kcc has moderate to high potential for moistureabsorption, with an average moisture content of 20%, a LL of 70%, and aLI of 3%. Kcw has the lowest capacity for moisture absorption, with anaverage moisture content of 15%, a LL of 55%, and a LI of −2%.

Results of plasticity testing and particle size analysis were combinedinto an activity chart showing the estimated clay mineralogy of theshale facies and FFT (FIG. 5). The shale facies are predominantlycomposed of montmorillonite with some illite. When compared to the claymineralogy testing, the results for Kca and Kcb are in generalagreement. However, the clay mineralogy test results for Kcc, Kcw, andFFT indicated higher levels of illite, which was not indicated by theactivity chart.

iii. Specific Gravity

Three samples of each shale facies and two samples of FFT were tested.The specific gravity of the shale facies fell within a range of2.68-2.82, with Kcw exhibiting the lowest value and Kca the highest. Thespecific gravity for Kca ranged from 2.78-2.82 and for Kcw from2.68-2.79. The specific gravity ranged from 2.74-2.80 and from 2.74-2.77for Kcb and Kcc, respectively. The average specific gravity was 2.80,2.77, 2.76, and 2.75 for Kca, Kcb, Kcc, and Kcw, respectively. The FFTsamples had a specific gravity of 2.35 and 2.36.

iv. Organic Content

One organic content test was performed for each shale facies and twoorganic content tests were performed on the FFT. Dean-Stark testing wasalso performed on the FFT to assess bitumen content. The organic contentwas about 2-3% for all facies. The FFT had an organic content rangingfrom 14.1-14.4%, and was composed of 93.0% minerals, 2.9% water, and4.1% bitumen.

v. Particle Size Distribution

Sieve and hydrometer analysis testing was performed on three samples ofeach facies and two samples of the FFT. Sand content is defined asparticles greater than 0.075 mm; silt as particles between 0.075 mm and2 μm; and clay as particles less than or equal to 2 μm. The highest claysize fraction was observed in Kca and Kcb, with lower clay content inKcc and Kcw. Kca contained 1.6% sand, 37.9% silt, and 60.5% clay, onaverage. For Kcb, the average results indicated 10.1% sand, 33.4% silt,and 56.5% clay. For Kcc, the average results indicated 1.3% sand, 59.2%silt, and 39.5% clay. For Kcw, the average results indicated 29.8% sand,36.3% silt, and 33.8% clay. For FFT, the average results indicated 1.2%sand, 51.8% silt, and 47.0% clay.

vi. Consolidation

One consolidation test was performed on a sample of the FFT. The samplewas moisture conditioned with fans to dry out the material prior to theinitial load increment to allow for proper placement of the materialinto the test mold. The FFT had an initial dry density of 833 kg/m³ (52pcf), an initial void ratio of 1.849, and exhibited a compression indexof 0.43 and a recompression index of 0.13. The coefficient ofconsolidation was measured for each load increment and was found to varyfrom 1.1×10⁻⁵ cm²/sec to 8.0×10⁻⁵ cm²/sec.

vii. Surface Area

To evaluate the variability of each shale facies relative to themoisture absorption capacity, one surface area test was performed foreach shale facies in accordance with the BET theory using a three pointanalysis of the dynamic flow technique. The samples were heated whilesimultaneously flowing gas over the sample to remove impurities. Thesamples were cooled and monitored for the volume of nitrogen gasabsorbed by the sample at three specific pressures (nitrogen gasphysisorption). The surface area of Kca was highest and closely followedby Kcb, while that of Kcw was the lowest (Table 3).

TABLE 3 Facies Kca Kcb Kcc Kcw Surface Area [m²/g] 46.5 43.7 24.8 10.7The results represent the surface area of the entire composition of eachshale facies. The surface area results do not correspond directly tospecific clay minerals, as the shale facies were found to consist ofmany different mineral components beyond the primary clay mineralcomponents of kaolinite, chlorite, illite, and montmorillonite.viii. Methylene Blue Index (MBI)

MBI testing measures the absorption of methylene blue dye by a claysample. Three samples of each facies were tested. The MBI of Kca and Kcbwere highest, while the MBIs of Kcc and Kcw were lowest (Table 4). TheMBI results represent the cation exchange capacity of the entirecomposition of each shale facies. The MBI results do not corresponddirectly to specific clay minerals, as the shale facies were found toconsist of a combination of different clay mineral components.

TABLE 4 Sample MBI [meq/100 g] Average MBI [meq/100 g] Kca-1 37.5 34.7Kca-2 39.5 Kca-3 27.0 Kcb-1 41.0 37.8 Kcb-2 48.5 Kcb-3 24.0 Kcc-1 16.018.2 Kcc-2 18.0 Kcc-3 20.5 Kcw-1 17.5 13.7 Kcw-2 16.0 Kcw-3 7.5ix. Mineralogy

One sample of each facies and one sample of the FFT were tested. X-raydiffraction (XRD) tests were completed both on the bulk fraction andclay-sized fraction, where the clay size fraction was defined as thematerial less than or equal to 3 μm in particle size. The results areset out in Table 5. The clay size fraction of Kca and Kcb was dominatedby montmorillonite and to a much lesser extent, illite. The clay sizefraction of Kcc and Kcw was primarily illite with some chlorite andkaolinite. The clay size fraction of FFT was predominantly kaolinitewith some illite. When compared to the estimated clay mineralogy basedon the clay activity chart (FIG. 5), these results compared well for Kcaand Kcw. However, when compared to Kcb and Kcc, the clay mineralogyresults indicated less montmorillonite than that predicted by theactivity chart. One Energy Dispersive X-Ray Spectroscopy (EDX) test wasconducted on the sample of Kcb and generally validated the XRD results.

TABLE 5 Sam- Weight ple Fraction [%] Kaolinite Chlorite IlliteMontmorillonite Kca Bulk 82.5 7 5 2 23 Clay 17.5 5 4 23 63 Bulk & 100.06 5 6 30 Clay Kcb Bulk 77.5 5 3 4 22 Clay 22.5 12 11 16 58 Bulk & 100.07 5 7 30 Clay Kcc Bulk 80.5 6 5 20 3 Clay 19.5 20 25 30 16 Bulk & 100.09 9 22 5 Clay Kcw Bulk 87.8 3 2 12 2 Clay 12.2 10 12 34 35 Bulk & 100.04 3 14 6 Clay FFT Bulk 83.0 34 0 21 0 Clay 17.0 76 0 18 0 Bulk & 100.041 0 21 0 Clayx. Bulk Density

Bulk density testing is defined as:ρ_(bulk) =m _(ps) /V _(ps)  (3)where ρ_(bulk)=bulk density; m_(ps)=mass of processed shale facies;V_(ps)=volume of processed shale facies. The bulk density was measuredfor both lump sizes of each of the four shale facies by measuring themass of shale required to fill a 1000 mL graduated cylinder (Table 6).

TABLE 6 Facies Lump Size Bulk Density [kg/m³] Kca coarse 937 fine 1,031Kcb coarse 906 fine 918 Kcc coarse 1,048 fine 1,020 Kcw coarse 1,096fine 1,117xi. Recycled Mine Water Testing

The recycled mine water had a resistivity of 260 ohm-cm and a pH of 7.9.

In summary, the results of the Atterberg limits, surface area, MBI, andclay mineralogy indicate that Kca and Kcb facies behave differently fromKcc and Kcw. Atterberg limits results indicate higher plasticity in Kcaand Kcb, while the same facies exhibit higher surface area than that ofKcc and Kcw. MBI values for Kca and Kcb are notably higher than those ofKcc and Kcw. The mineralogy of Kca and Kcb indicates highermontmorillonite content than that measured in Kcc and Kcw. Without beingbound by any theory, the mineralogy of the shale facies (which isrelated to the plasticity, surface area, and MBI) controls the moisturetransfer phenomena and, thus, the strength of the mixtures. The indextest results tend to indicate a linear relationship in that higher LLand PI, higher clay size fraction, lower moisture content, and highersurface area correlate to larger absorption capacity, larger MBI, andmore montmorillonite content.

EXAMPLE 3 Preparation of Shale/FFT Mixtures

Shale/FFT mixtures were prepared to include specific shale facies, shalelump size, and FFT:shale ratio. The mixing process involved onetechnician placing the processed shale in a large plastic mixing binwhile another poured FFT into the bin. A third technician mixed theshale and FFT using a metal spoon and spatula, while retaining the shalelump size and preventing inadvertent compaction. Portions of the FFT andshale were placed in the sample mixing bin in a total of 8 to 10 liftsto ensure thorough mixing. Mixing was completed in 10-15 minutes in atemperature-controlled room. The sample containers were covered withplastic immediately to minimize moisture loss. Each FFT-shale mixturewas placed into a test mold (6 mm thick acrylic cylinder having adiameter of 254 mm and height of 178 mm) for vane shear testing. Themixture was placed into the test mold to a height of 152 mm to allow for25 mm of splash clearance. The mixture was placed into the test mold inapproximately 6 to 8 lifts by one technician, while a second techniciancarefully used a spatula to spread out each lift and prevent thecreation of significant voids in the test mold, while avoidinginadvertent compaction. Lifts were placed maintaining a relatively flatsurface and the final lift was used to create a relatively flat surfacealong the top of the sample. As part of the mixing process, a smallsample of the mixture was placed separately into a glass jar (40 mm indiameter and 150 mm in height) for independent suction measurements.

EXAMPLE 4 Testing of Shale/FFT Mixtures

i. Shear Strength

The undrained shear strengths of various FFT-shale mixtures wereevaluated using vane shear testing. The magnitude, rate, and mechanismsof the undrained shear strength increase that occurs under different mixratios, shale facies, shale lump size, and time were determined. Threedifferent ratios of FFT:shale (0.2:1.0, 0.4:1.0, and 0.6:1.0 based onbulk volume) were tested. A ratio of 0.5:1.0 was specified for acomposite sample formed of 50% Kcc, 30% Kcb, and 20% Kca (by bulkvolume). Table 7 provides a summary of the vane shear testing.

TABLE 7 Mix Coarse Lump Size Fine Lump Size Facies ratio 1 2 3 7 14 1 23 7 14 Kca 0.2 x x x x x x x x x x 0.4 x x x x x x x x x x 0.6 x x x x xx x x x x Kcb 0.2 x x x x x x x x x x 0.4 x x x x x x x x x x 0.6 x x xx x x x x x x Kcc 0.2 x x x x x x x x x x 0.4 x x x x x x x x x x 0.6 xx x x x x x x x x Kcw 0.2 x x x x x x x x x x 0.4 x x x x x x x x x x0.6 x x x x x x x x x x Composite 0.5 x x x x x x x x x x Layered 0.6N/A N/A Absorption N/A N/A N/A

Five shear strength tests were performed on each sample to assess thepotential shear strength gain over time as moisture was transferred fromthe FFT to the shale. The vane shear apparatus was a Geomil™ FFL 100Electrical Vane Shear Tester capable of delivering a maximum torque of100 N-m under and constant rate of rotation of 0.1 degrees per second.This rate of rotation allowed for measurement of the undrained shearstrength, as slower rates of rotation may allow pore pressures todissipate and not represent undrained conditions. Device control wasperformed through a computer running Geomilspecific™ Microsoft Excelspreadsheet connected to the vane shear apparatus, and vane torque datawere acquired at an approximate frequency of 1 Hz. All tests wereperformed utilizing a Geomil™ 70 mm×35 mm vane which was selected toallow for proper assessment of the undrained shear strength of themixture as a function of the shale lump size. The vane was sufficientlylarge such that the size of the lumps within the sample mixture did notimpact the vane shear results. Vane shear tests utilizing vanes that aresimilar in size to the shale lumps produce erroneous results thatgenerally do not represent the undrained shear strength of the mixture.

Sample molds were placed on a steel table and moved manually to allowfor tests in five locations within the mold. The test locations werespecified at 72-degree radial spacing within each test mold. Testlocations were specified to allow for sufficient spacing to avoidimpacts between each test. Test order was specified such that eachsubsequent test was performed on the opposing side of the test mold toavoid subsequent adjacent tests. Each shale-FFT mixture was tested atfive time intervals (1, 2, 3, 7 and 14 days) to determine if the shearstrengths of the mixtures might increase over time.

Following completion of the 14 day vane shear test, each mixture wasre-compacted to both reduce voids with the material and to simulatefield compaction during placement. Compaction was not successfullycompleted on all samples. Where feasible, two different compactionlevels were specified. Samples were placed in standard Proctor densitymolds and compacted in four lifts. The lower compaction level included14 blows/lift with a standard Proctor hammer, while the highercompaction level included 28 blows/lift with the same hammer. The energyused to compact each sample was 139 kN-m/m³ (2,896 ft-lbf/ft³) and 277kN-m/m³ (5,792 ft-lbf/ft³) for the low and high compaction levels,respectively. Vane shear tests were completed on compacted samplesimmediately following compaction.

Each vane shear test was performed to a sufficient amount of rotationbeyond the peak value (90-180°) to allow for adequate determination ofthe peak undrained shear strength of the mixture. The results are shownin FIGS. 6-16 which indicate the peak undrained shear strength measuredin each test. FIGS. 6-10 show the variation in peak undrained shearstrength over time following mixing, FIGS. 11-14 indicate the change inpeak undrained shear strength under varying levels of compaction onmixtures where compaction was feasible.

The results of the peak undrained shear strength indicated that theundrained shear strength was consistently higher for samples with lowermixing ratio (i.e. lower FFT content). The samples containing 0.2 unitsof FFT exhibited the highest undrained shear strength (14-33 kPa), whilethose with 0.6 units of FFT had the lowest undrained shear strength (1-7kPa). The undrained shear strength of the 0.4 unit FFT (4-26 kPa) wasonly slightly higher than those of the 0.6 unit FFT. The mostsignificant increase in undrained shear strength was observed whencomparing 0.4 FFT to 0.6 FFT. FIG. 15 shows the relationship between FFTcontent and the corresponding undrained shear strength at 14 daysfollowing mixing.

An undrained shear strength of 5 kPa was achieved for all Kca samples,with the exception of the 0.6 FFT, coarse shale mixture. Similarly, 5kPa was achieved for Kcb, Kcc, and Kcw at 0.2 FFT for both fine andcoarse shale lumps. This requirement was also achieved in the Kcc, 0.4,coarse and Kcw, 0.4, fine mixtures. These results generally indicatethat a mixing ratio of 0.2 will achieve an undrained shear strength ofat least 5 kPa. Conversely, a mixing ratio of 0.6 is unlikely to exhibitat least 5 kPa undrained shear strength.

The mixtures with Kca exhibited the highest overall undrained shearstrength (33 kPa, 0.2 FFT, fine). The results were somewhat mixed forsamples with 0.2 units FFT, while results for samples with 0.4 and 0.6units FFT generally indicated that the Kca mixtures yielded the highestundrained shear strengths. FIGS. 15-16 show the peak undrained shearstrength for each of the shale facies.

Of the samples containing 0.2 units FFT and fine shale lumps, themixtures with Kca had the highest undrained shear strength at 33 kPa,followed by Kcw, Kcb, and Kcc (22 kPa, 20 kPa, and 18 kPa,respectively). Conversely, of the samples with 0.2 units FFT and coarseshale lumps, Kcc exhibited the highest undrained shear strength at 22kPa, followed by Kcb (17 kPa), and Kca and Kcw (14 kPa).

For those samples with 0.4 and 0.6 units FFT, Kca exhibited the highestundrained shear strength for both fine and coarse shale lumps. Theresults were generally mixed for the remaining shale facies, with nosignificant trend for a specific facies outperforming other facies,aside from Kca. At 0.4 units FFT and fine shale lumps, the highestundrained strength was observed for the sample with Kca at 26 kPa, whilethe remaining shale facies had undrained shear strengths between 4-7kPa.

Similarly, coarse shale lumps and 0.4 units FFT yielded the highestundrained shear strength in Kca (9 kPa), while the other shale faciesexhibited undrained shear strengths ranging from 4-5 kPa. At 0.6 unitsFFT and fine shale lumps, the highest undrained strength was observedfor the sample with Kca at 7 kPa, while the remaining shale facies hadundrained shear strengths between 1-2 kPa.

Similarly, coarse shale lumps and 0.4 units shale yielded the highestundrained shear strength in Kca (4 kPa), while the other shale faciesexhibited undrained shear strengths ranging from 2-3 kPa.

When correlated to the clay mineralogy, the results of Kca generallytend to indicate that a higher montmorillonite content correlates to ahigher undrained shear strength, likely since a high montmorillonitecontent corresponds to a high ability to hold water. This trend ispartially validated by the results of Kcc and Kcw, where themontmorillonite content is low and the undrained shear strength is lower(relative to Kca). However, this is contradicted by the results of Kcb,which has a high montmorillonite content (close to Kca), but does notexhibit the same high undrained shear strengths of Kca. This phenomenonis closely mirrored in the clay surface area, where high surface areagenerally correlates to high undrained shear strength and vice versa.Similarly, the trend is not observed with Kcb, where the surface area isrelatively high and but undrained shear strength is lower than that ofKca. This discrepancy may be due to the effects of other factors such asmixture moisture content, which may dominate the overall behavior of thematerial.

The size of shale lumps had a mixed effect on the undrained shearstrength of the mixtures. For samples with 0.2 units FFT, a higherundrained shear strength was observed for the fine shale lumps of allfacies except Kcc. A noticeable increase in undrained shear strength wasalso observed in the fine Kca, 0.4 FFT sample. Of the remaining samples,no significant increase in the undrained shear strength was observed forthe fine shale lumps versus the coarse shale lumps. In general, theresults indicated that smaller shale lumps result in a noticeableincrease in the undrained shear strength for those samples with less FFT(0.2 units). The smaller shale lumps had no significant effect(increase) in the undrained shear strength for most of the samplescontaining 0.4 and 0.6 units FFT. FIG. 16 shows the relationship betweenshale lump size and the corresponding undrained shear strength.

Of the samples containing fine shale lumps, all of the 0.2 FFT mixturesand Kca and Kcc of the 0.4 FFT mixtures exhibited undrained shearstrengths of at least 5 kPa. For mixtures with coarse shale lumps, allof the 0.2 FFT mixtures, the 0.4 FFT mixtures of Kca and Kcw, and the0.6 FFT mixture of Kca exhibited undrained shear strengths of at least 5kPa.

When correlated to the surface area, the results do not provide a clearcorrelation to strength. This discrepancy could be due to the effects ofother factors such as mixture moisture content, which may dominate theoverall behavior of the material.

Plots of the undrained shear strength variation over time are includedin FIGS. 6-10. In a majority of mixtures, the results indicated that nosignificant increase in the undrained shear strength was observedthroughout the time interval tested. A slight increase in undrainedshear strength was observed in both the fine and coarse shale lumps ofthe 0.2 FFT mixtures for Kca and Kcw. However, the undrained shearstrength increase observed in these cases was not significant and it ispossible that the observed increase is simply associated with the noisein the data. Although no significant undrained shear strength increasewas observed in a majority of the mixtures, it is likely that a majorityof the shear strength increase occurred within the initial 24 hoursfollowing mixing.

The results of the undrained shear strength variation with compactionare included in FIGS. 11-14. Compaction was most successful on the Kcamixtures, with all three mix ratios and both shale lump sizessuccessfully compacted. Compaction was successfully performed on theremaining shale facies on both the coarse and fine shale lumps of the0.2 and 0.4 FFT ratios. The higher level of compaction was accomplishedon the 0.2 FFT ratio (fine and coarse) for all four shale facies and onthe 0.4 FFT ratio of the fine Kca. In general, compaction was mosteffective on mixtures with low FFT content, small shale lumps, andhigher plasticity shale.

The undrained shear strength was successfully increased throughcompaction of the 0.2 and 0.4 FFT ratios of Kca (both coarse and fine).Strength improvement was also observed for the coarse and fine shalelumps of the 0.2 FFT ratio for the remaining shale facies. Additionalstrength improvement was observed with the higher level of compaction onthe 0.2 (coarse and fine) and 0.4 (fine) mixtures of Kca. No additionalstrength improvement was observed at the higher compaction level for theremaining shale facies.

Standard Proctor tests were performed on two samples of the Kca fine 0.2and Kcw coarse 0.4 mixtures to determine the dry density moisturecontent relationship, and the maximum dry density and optimum moisturecontent. The Kca fine 0.2 mixture had a moisture content of 29%, anoptimum moisture content of 26%, and a maximum dry density of 1,493kg/m³ (93 pcf). The Kcw coarse 0.4 mixture had a moisture content of35%, an optimum moisture content of 17%, and a maximum dry density of1,690 kg/m³ (106 pcf). The Kca fine 0.2 mixture had much higherundrained shear strength (33 kPa) than did the Kcw coarse 0.4 mixture (5kPa).

Composite mixtures were created from Kca (20%), Kcb (30%), and Kcc (50%)to understand the effects of both coarse and fine shale lumps at a ratioof 0.5 units FFT. The results indicate a long-term undrained shearstrength of approximately 4.7 kPa (fine) and 3.7 kPa (coarse) (FIGS. 10,15 and 16). These results were, in general, less than those of Kca andKcc and very similar to those of Kcb at a OA FFT ratio. Similarly, theresults of the composite sample were less than Kca, but greater than Kcband Kcc at a 0.6 FFT ratio. While the results on the composite samplesdid not yield an undrained shear strength of at least 5 kPa, they didindicate promise that this requirement may be met with slightly lowerFFT ratios with the same shale composition.

ii. Moisture Transfer Measurement

The Liquid Limit is an index property of a soil that indicates theability of the soil/clay particles to hold water. Since the FFT has amoisture content (132%) higher than the Liquid Limit (72%), it hasexcess water which leads to a soft consistency and little strength.Conversely, the shale has a high Liquid Limit (60-130%) and lowermoisture content (15-28%). As a result, the shale exists with a deficitof water and has the ability to absorb water. The moisture transfer fromFFT to shale was evaluated with respect to shale facies, lump size, FFTmix ratio, and time.

FFT moisture content tests were conducted at intervals of 0, 1, 2, 3, 4,8, 12, and 24 hours during the initial 24-hour period following mixing.FFT moisture contents were collected daily or twice daily. FFT/shalemixture moisture contents were collected on daily or twice daily. Themoisture content was measured utilizing three different methods. Methods1 and 2 performed moisture content tests directly on the vane shear testmixtures. Method 3 performed moisture content tests on the FFT, but onseparate samples developed specifically to elucidate the moisturetransfer between the FFT and shale. Method 4 assessed the absorptioncapacity of the shale lumps/facies. Table 8 summarizes the moisturetransfer testing.

TABLE 8 Mix Facies ratio Coarse Fine Kca 0.2 X² X² 0.4 X^(1,2) X² 0.6X^(1,2) X² Kcb 0.2 X² X² 0.4 X² X² 0.6 X² X² Kcc 0.2 X² X² 0.4 X² X² 0.6X² X² Kcw 0.2 X^(1,2) X² 0.4 X^(1,2) X² 0.6 X^(1,2) X² Composite 0.5Layered 0.6 X³ X³ Absorption N/A X⁴ X⁴ ¹Method 1, ²Method 2, ³Method 3,⁴Method 4Method 1—FFT Moisture Content

Samples of the FFT/shale mixture were collected manually from theprimary vane shear test molds. Attempts were made to remove the shalelumps from the mixture sample until only FFT appeared to remain. Theremaining FFT sample was then tested for moisture content. FFT moisturecontent tests were initially planned to be performed on all samples.However due to difficulties associated with collecting a pure FFTsample, the moisture content tests on mixtures with fine shale lumpswere eliminated as the shale lumps could not be removed from the mixturefor the test samples. Results of FFT moisture content testing for Kcaand Kcw (coarse) are shown in FIGS. 19 and 22. The results weregenerally erratic and the remaining FFT moisture content tests(Method 1) were removed. However, data in FIGS. 19 and 22 show that themoisture content of the mixture does not change significantly over timeindicating that the temperature and humidity controlled room andprocedure were successful in maintaining the moisture of the mix.

Method 2—FFT/Shale Moisture Content

Samples of the FFT/shale mixture were collected from the primary vaneshear test molds,

The FFT/shale samples were then tested for moisture content. The resultsindicate that the moisture content was constant for each mixture (FIGS.19-20). This provided an indication that laboratory conditions (i.e.temperature control, plastic seal) helped to minimize drying of thesamples.

Method 3—FFT Moisture Content and Solids Content

Due to the difficulties associated with collecting reliable samples forMethod 1, an alternate procedure was developed for determining the levelof moisture within the FFT portion of the mixture. The testing waslimited to coarse shale lumps of Kca and Kcw at a 0.6 FFT ratio. Thesamples were prepared using the same acrylic test molds as were used inthe vane shear testing program. However, the FFT was placed inapproximately 12 lifts of equal thickness with layers of shale placed inbetween the FFT layers. The shale was deposited in a manner to create agenerally homogenous mixture of shale and FFT. Samples of the FFT werecollected for moisture content testing using a 5 mm diameter rod.

Method 4—Shale Moisture Absorption Testing

Absorption testing was performed to assess the rate of moistureabsorption and the overall moisture capacity. Samples of the shalefacies (fine and coarse lump sizes) were placed on filter paper bearingon plastic mesh containers. Each shale sample weighed approximately45-50 g and was spread evenly across the containers such that the shalewas no more than 2-4 mm thick and 100 mm in diameter. Samples wereplaced in a humidity chamber maintaining a constant level of 100%humidity. One control sample consisting of filter paper and a plasticmesh container was also placed in the humidity chamber. Samples weremeasured for total mass to determine the associated sample moisturecontent at 0, 0.5, 1, 1.5, 2, 3, 4, 8, 12, 24, 36, 48, 60, and 72 or 144hours. Moisture content of the shale lumps was determined. Moisturecontent results from the shale absorption testing utilizing Method 4 areincluded in FIGS. 27-28.

iii. Solids Content

Solids content is defined as:S _(c)=1/1+w  (4)where S_(c)=solids content and w=geotechnical moisture content. Resultsof the FFT moisture content and solids content tests utilizing Method 3are shown in FIGS. 23-26.

In summary, Method 1 was found to be unreliable (FIGS. 19 and 22).Multiple measurements via Method 2 were unnecessary. Since no moisturewas allowed to evaporate from the samples, the moisture content of themixture did not vary (FIGS. 19-22). Some of the results from Method 2indicated a potential correlation between the moisture content of themixture and the corresponding optimum moisture content. The Kca fine 0.2mixture had a moisture content of 29% and an optimum moisture content of26%, while the Kcw coarse 0.4 mixture had a moisture content of 35% andan optimum moisture content of 17%. The Kca fine 0.2 mixture had a muchhigher undrained shear strength (33 kPa) than did the Kcw coarse 0.4mixture (5 kPa). These findings indicate a potential correlation betweenthe moisture content of the mixture and corresponding optimum moisturecontent. Mixtures having moisture content close to the optimum moisturecontent resulted in higher undrained shear strength than those withmoisture contents significantly above the optimum moisture content.Mixtures placed near the optimum moisture content could achieve higherlevels of compaction in a mine application.

In contrast, the results of Method 3 indicated a consistent reduction inthe FFT moisture content. Method 3 specifically focused on the moisturetransfer mechanism and the mixtures were not used for laboratory vaneshear testing. Two samples were tested using Method 3, Kca and Kcw bothcoarse shale lumps at a 0.6 FFT ratio. The variation in FFT moisturecontent over time is shown in FIGS. 23-24, while FIGS. 25-26 show theassociated variation in FFT solids content over time. The results showeda FFT moisture content reduction of approximately 80% for both Kca andKcw. The corresponding FFT solids content increased roughly 25% to67-70% for both Kca and Kcw. A majority of the moisture contentreduction occurred in the initial 24-hour period following mixing, whichgenerally agrees well with the suction results. No significantdifference was observed between the two shale facies tested utilizingMethod 3 which was only employed on mixtures with coarse shale particlesand high FFT content. Similar success may not be achievable on mixtureswith smaller shale particles with low FFT content.

To assess the moisture capacity of the shale particles, absorptiontesting was performed using Method 4. This method did not use FFT andinstead focused on an evaluation of the shale moisture content while ina humidity chamber. Tests were performed on all four shale facies,evaluating both coarse and fine lump sizes. The results of the shaleabsorption tests are shown in FIGS. 27-28. The results indicated thatKca consistently had the highest capacity to absorb moisture, exhibitingapproximately 80% moisture with coarse lumps and 90% moisture with finelumps. For the coarse shale lumps, Kcb exhibited the next highestmoisture capacity at 60% moisture, but had the lowest capacity at 50%moisture in the fine lumps. The Kcc and Kcw were similar in each test,with approximately 45% moisture with coarse lumps (the lowest of theresults on coarse shale lumps) and 60% moisture with fine lumps. Ingeneral, the results indicated a 10-15% increase in moisture capacitywith a reduction in lump size, although the results of Kcb indicated thereverse of this trend. While these results could not be directlycorrelated to the FFT moisture content results of Method 3, they didindicate the shale absorbs a majority of the moisture within the initial24-hour period, which agrees well with the results of Method 3 and thesuction measurements. The results also showed that Kcb, Kcc, and Kcwexhibited the highest rate of increase in moisture content during theinitial 24 hours of the test, while Kca increased in moisture at aslightly slower rate but reached a higher capacity at the end of thetest.

iv. Suction

Suction testing was performed to assess the moisture tension thatdeveloped within the FFT/shale mixture under non-saturated conditionsusing tensiometers inserted into the sample mixtures. Tensiometermeasurements were collected on a continuous basis during the initial24-hour period following mixing for each sample. After the 24-hourperiod, spot tensiometer measurements were collected on some of thesamples on a daily or twice daily basis. Moisture tension measurementswere performed to correlate the moisture transfer within the FFT-shalemixture. Tension measurements were completed on a separate sample ofeach mixture prepared during the primary mixing process. Table 9summarizes the suction testing.

TABLE 9 Mix Coarse Lump Size Fine Lump Size Facies ratio 1 2 3 7 14 1 23 7 14 Kca 0.2 x x x x x x x x x x 0.4 x x x x x x x x x x 0.6 x x x x xx x x x x Kcb 0.2 x x x x x x x x x x 0.4 x x x x x x x x x x 0.6 x x xx x x x x x x Kcc 0.2 x x x x x x x x x x 0.4 x x x x x x x x x x 0.6 xx x x x x x x x x Kcw 0.2 x x x x x x x x x x 0.4 x x x x x x x x x x0.6 x x x x x x x x x x Composite 0.5 x x x x x x x x x x Layered 0.6 xx Absorption N/A N/A N/A

The moisture tension measurements were performed using Decagon™ T5xtensiometers connected to a Campbell Scientific CR1000datalogger. TheT5x tensiometers used in this study had a tip diameter of 5 mm and shaftlength of 100 mm. Device control was performed through a computerrunning Campbell Scientific software connected to the datalogger.Tensiometer measurements were collected every 5 minutes for the initial24-hour period following mixing. Suction measurements were performed onall primary mixtures, the composite sample mixtures, and on the layeredsamples developed as part of moisture transfer Method 4. FIGS. 17-18show the long term or maximum suction observed in each primary andcomposite mixture during the initial 24-hour period of continuous datacollection.

In all cases, the highest levels of suction were observed in the sampleswith the lowest FFT content. Higher suction was also generally observedin the finer shale lumps. Kca consistently yielded the highest levels ofsuction, while Kcw tended to create the least amount of suction. Suctionat the 0.2 FFT ratio ranged from 14 kPa (Kcc, coarse) to 71 kPa (Kca,fine). This high level of suction is primarily due to a high surfacearea relative to the level of FFT within the samples. The 0.2 FFT ratiomixtures yielded unsaturated soil conditions and the finer shale lumpscreated a higher ratio of surface area to volume. The results of thesuction testing on the 0.4 FFT ratio mixtures indicated significantlyreduced suction, with results ranging from 2 kPa (Kcc, coarse) to 31 kPa(Kca, fine). The lowest suction results were observed in the 0.6 FFTratio mixtures, with results ranging from −0.6 kPa (Kcw, fine—likelydata noise) to 6 kPa (Kca, coarse). The highest suction levels wereobserved in Kca and these results are likely attributed to thesignificant moisture capacity that exists primarily within Kca.

In general, the suction increased significantly within the initial 12 to24 hour period following mixing. Suction was generally constant orexhibited a constant rate of increase 24 hours after mixing. Theseresults indicate that a majority of the moisture transfer occurs withinthe initial 12 to 24 hours after sample mixing. This phenomenon agreedwell with the observation that no substantial increase in undrainedshear strength was observed after 24 hours following mixing.

EXAMPLE 5 Testing of Larger Shale Lumps/FFT Mixtures

Testing was conducted using clay-shale lumps (samples of Kca, Kcb, Kccand Kcw facies) of large size (+19.00 mm and −19.00+4.75 mm) and smallsize (−4.75+2.00 mm and −2.00 mm). Samples of FFT, recycle water, andsaline water were also collected. Index tests were performed to assessvarious properties of the shale facies and FFT, namely moisture content,solids content, organic content, bulk density, specific gravity,particle size distribution by hydrometer, surface area with nitrogen asadsorbate, Methylene Blue Index, and X-Ray Diffraction. Results aresummarized in Tables 10 and 11. The FFT samples had approximately 43 wt% of solids content and 98% fines (less than 44 μm). The solids contentof the FFT sample was slightly higher than the solids content of samplesused in the previous tests.

TABLE 10 Moisture True Bulk Density Fines Clay content Liquid PlasticPlasticity Density (kg/m³) (% (%) Material (%) Limit Limit Index (kg/m³)4.75-2 mm −2 mm −44 μm) −2 μm Kca 18.5 124.1 23.4 100.7 2,800 937 1,03197.0 60.0 Kcb 28.5 115.5 23.2 92.3 2,770 906 918 85.0 54.0 Kcc 20.1 70.118.9 51.2 2,757 1,048 1,020 99.0 40.0 Kcw 14.8 55.1 16.0 39.1 2,7501,096 1,117 62.0 34.0 FFT 132.5 71.8 22.5 49.4 N/A N/A N/A 98.0 46.0

TABLE 11 Clay- Silt Natural shale Gravel Sand (%) Clay Moisture SoilSample Oil Water Solids Liquid Plastic Plasticity (%) (%) 2- (%) ContentUnit Number (%) (%) (%) Limit Limit Index +4.75 mm 4.75-2 mm 0.002 mm −2μm (%) Kca 1 1.20 12.52 86.28 101.1 23.1 78.0 0.3 5.2 39.9 54.6 19.6 295.1 22.0 73.1 0.0 1.6 40.9 57.5 22.9 3 101.5 24.6 76.9 0.0 0.8 47.451.8 24.6 Kcb 1 107.4 23.4 83.9 0.0 8.4 38.3 53.3 22.3 2 67.6 21.3 46.20.0 5.7 42.1 52.2 22.8 3 117.4 29.7 87.7 0.0 0.4 30.6 69.0 29.7 Kcc 170.5 21.7 49.3 0.3 2.2 57.0 40.5 18.5 2 74.8 21.3 54.0 0.0 0.8 49.2 50.021.7 3 92.0 25.4 66.6 0.0 0.2 46.8 53.0 23.6 Kcw 1 2.44 8.83 88.71 42.417.4 25 0.4 35.3 35.6 28.8 16.5 2 5.70 13.24 81.06 52.3 18.3 34 0.1 31.936.6 31.5 17.4 3The recycle water sample was analyzed for pH and electrical resistivity.The water chemistry of the saline water was analyzed (Table 12).

TABLE 12 pH 7.4 Conductivity 5660 μS/cm Total Dissolved Solids 3792.2ppm Chloride 1130 mg/L Sulfate 488 mg/L Bicarbonate 1179 mg/L Carbonate966.4 mg/L Calcium 165 mg/L Potassium 18.8 mg/L Sodium 1033 mg/LShale/FFT mixtures were prepared as described in Example 3 to includespecific shale facies, shale lump size, and FFT:shale ratio (0.2:1.0,0.4:1.0, and 0.6:1.0).i. Moisture Transfer Measurement

The moisture transfer of water vapour to the clay-shale lumps was basedupon the variation in the solids content (wt %) of FFT over time. Theclay-shale particles and FFT fines were distinguishable when largersizes of clay-shale lumps were used. Regardless of the size of theclay-shale lumps, the solids content of the FFT increased significantlywithin the initial 24 hours and then increased moderately, eventuallyreaching a maximum after one week (FIGS. 29-31). Since plastic film wasused to prevent moisture loss from the samples, it is believed that theincrease in the solids content of FFT was a consequence of moisturetransfer. FIG. 31 shows the solids content of the FFT over a three monthperiod. As the solids content of FFT hardly increased one week after themixing, a longer retention time did not appear to promote the moisturetransfer from the FFT to the clay-shale lumps.

ii. Suction

Suction testing was performed to assess the moisture tension thatdeveloped within the FFT/shale mixture under non-saturated conditionsusing a tensiometer (UMS T5x Tensiometer) inserted into the samplemixtures. Similar to the solids content of the FFT, the suctionincreased significantly following mixing, and leveled off within theinitial 24 hours after mixing, suggesting that moisture transfer fromthe FFT to the clay lumps occurred within the initial 24 hours (FIGS.32-35). Suction is the force needed for absorption of moisture fromsurrounding materials. A positive suction pressure indicates thepresence of free pore water. Although the suction was negative, thesuction increased with the volumetric mixing ratio. At a 0.6 FFT ratio,the suction was close to zero, indicating the possibility of thepresence of free pore water in the FFT and clay-shale mixtures when theratio is increased above 0.6. A FFT ratio between 0.2 and 0.4 is thuspreferable.

iii. Shear Strength

The undrained shear strengths of various FFT-shale mixtures wereevaluated using vane shear testing (35 mm diameter, 70 mm height labvane; and a 10 mm diameter, 17.6 mm height lab vane). For each mixture,the first vane shear testing was conducted 24 hours after mixing. Theshear strength did not increase over time, suggesting that moisturetransfer from the FFT to the clay lumps occurred within the initial 24hours (FIGS. 36-40). For Kcb, Kcc and Kcw, the shear strengths wereclose to or below 5 KPa when the FFT ratio was greater than or equal to0.4.

The mixtures were compacted to reduce voids within the material, with aProctor compaction test performed two weeks after mixing. FIGS. 41-44show the effect of compaction on shear strength. The energy used tocompact each sample was 2,896 ft-lbf/ft³. A higher compacting energyhardly increased the shear strength. At the FFT ratios of 0.2 and 0.4,compaction significantly increased the shear strength of the mixturesabove 5 KPa. The effect of compaction was negligible at the FFT ratio of0.6. The Kca-FFT mixture exhibited the highest suction and the greatestgain in shear strength after compaction.

iv. Testing of a Composite Clay-Shale Sample

A composite sample was formed of 20% Kca, 30% Kcb and 50% Kcc (bulkvolume), with the ratio representing the approximate thickness ofclay-shale overburden for each facies in a mine. The compositeclay-shale lumps were mixed with the FFT at a higher FFT ratio (0.5).The shear strength of the mixtures did not change over time, suggestingthat moisture transfer from the FFT to the composite clay-shale lumpsoccurred within the initial 24 hours (FIG. 45). The shear strength wasslightly less than 5 KPa. As the composite mixtures at a 0.5 FFT ratiowere too wet to compact, no gain in the shear strength could beobtained.

v. Use of Saline Water

A saline water sample was used to determine the feasibility of applyingco-mixing to the sequestration of saline aqueous fluid waste. FIG. 46shows the undrained shear strength of the composite saline water andclay-shale mixtures. When mixed at FFT ratios less than 0.4, thecomposite mixtures achieved undrained shear strengths above 5 KPa within48 hours without compaction, suggesting that co-mixing has the potentialto sequestrate saline aqueous fluid waste inside the clay-shaleoverburden waste dump.

vi. Moisture Absorption Capacity of Clay-Shale

To assess the moisture capacity of the shale particles, absorptiontesting was performed using two methods, namely use of a humiditychamber to observe the increase in the mass of clay-shale lumps (Example4), and determination of an increase in the solids content of the FFTinto which large-sized clay-shale lumps (−50+19 mm) were immersed.

FIGS. 47 and 48 show the moisture absorption capacity based on thesurface area of the clay-shale lumps, assuming the clay-shale lumps(−4.75+2.00 mm) are identical spheres of 3.375 mm diameter. Theabsorption of FFT pore water onto the clay lumps slowly occurs only onthe surface of the clay lumps. The moisture transfer capacity variedbetween 0.5 and 1.7 kg/m² depending on the facies with Kca having thehighest value. The majority of the moisture transfer to the clay lumpsoccurred within the initial 24 hours.

The results of the humidity chamber testing in which the smallclay-shale lumps were exposed to water vapor indicated a slightlysmaller moisture absorption capacity per net surface area as comparedwith results of large clay-shale lumps soaked into the FFT. Thediscrepancy may have resulted from the difference in the sizes of theclay-shale lumps.

FIG. 49 shows the decrease in the solids content at the centre of thelarge clay-shale lumps, indicating the moisture transfer may reach atleast 1 inch deep into the clay-shale lumps. The clay-shale samples usedin the humidity chamber test may have been too small for thedetermination of the moisture absorption capacity. The moistureabsorption capacity obtained from the large clay-shale testing variedfrom 3.5 to 4.2 kg/m². This result also suggests that it may not benecessary to crush clay-shale overburden to less than 2 inches.

EXAMPLE 6 Overburden (Kca) Added to FFT Centrifuge Cake

FIG. 50 shows the increase in undrained shear stress (KPA) of theoverburden/FFT centrifuge cake mixture versus the weight percent of thesolids in the mixture. It can be seen in FIG. 50 that increasing theproportion of overburden (i.e., increasing the wt % of solids) resultedin a significant increase in undrained shear strength.

The overburden/FFT centrifuge cake deposit may be collected andtransported via a conveyor, pump or transport truck to a disposal area.At the disposal area, the overburden/FFT centrifuge cake deposit isstacked to maximize dewatering by natural processes includingconsolidation, desiccation and freeze thaw via 1 to 2 m, or greater than2 m thick annual lifts to deliver a trafficable surface that can bereclaimed.

In another embodiment, the overburden/FFT centrifuge cake deposit may beplaced in layers which alternate with layers of compacted lifts. In oneembodiment, the compacted lifts comprise sand. Such a configuration oflayers not only delivers a trafficable surface but also facilitatesdrainage. In another embodiment, poldering can be used. A polder is alow-lying tract of land enclosed by embankments (barriers) known asdikes that forms an artificial hydrological entity.

From the foregoing description, one skilled in the art can easilyascertain the essential characteristics of this invention, and withoutdeparting from the spirit and scope thereof, can make various changesand modifications of the invention to adapt it to various usages andconditions. Thus, the present invention is not intended to be limited tothe embodiments shown herein, but is to be accorded the full scopeconsistent with the claims, wherein reference to an element in thesingular, such as by use of the article “a” or “an” is not intended tomean “one and only one” unless specifically so stated, but rather “oneor more”. All structural and functional equivalents to the elements ofthe various embodiments described throughout the disclosure that areknown or later come to be known to those of ordinary skill in the artare intended to be encompassed by the elements of the claims. Moreover,nothing disclosed herein is intended to be dedicated to the publicregardless of whether such disclosure is explicitly recited in theclaims.

REFERENCES

The following references are incorporated herein by reference (wherepermitted) as if reproduced in their entirety. All references areindicative of the level of skill of those skilled in the art to whichthis invention pertains.

-   BGC Engineering Inc., 2010. Review of Reclamation Options for Oil    Sands Tailings Substrates. Oil Sands Research and Information    Network, University of Alberta, School of Energy and the    Environment, Edmonton, Alberta. OSRIN Report No. TR-2. 59 pp.-   Chapman, D., Barbour, S. L. and O'Kane, M., 2006. Hydrogeology of    South Bison Hill. 7^(th) International Conference on Acid Rock    Drainage (ICARD), Mar. 26-30, 2006.-   Chapman, D. E., 2008. Hydrogeologic Characterization of a Newly    Constructed Saline-Sodic Clay Overburden Hill. University of    Saskatchewan Thesis.

Isaac, B. A., Dusseault, M. B., Lobb, G. D., and Root, J. D. 1982.Characterization of the Lower Cretaceous Overburden for Oil SandsSurface Mining Within Syncrude Canada Ltd. Leases, Northeast Alberta,Canada. Proceedings 4th Congress International Association ofEngineering Geology. New Delhi, India, 1982, 14 p.

-   Lord, E. R. and Isaac, B. A., 1989. Geotechnical Investigations of    Dredged Overburden at the Syncrude Oil Sand Mine in Northern    Alberta, Canada. Canadian Geotechnical Journal, 26, 132-153.-   Lord, E. R. F., Maciejewski W., 1995. Codisposal of fine tails and    overburden utilizing pipelining techniques. Mine Planning and    Equipment Selection 1995: Proceedings of the Fourth International    Symposium on Mine Planning and Equipment Selection/Calgary/Canada/31    Oct.-3 Nov. 1995, Page 973-987.-   Mellon, G. B. and Wall, J. H. 1956. Geology of the McMurray    Formation. Research Council of Alberta, Report No. 72,-   Mimura, D. W., 1990, Shear Strength of Hydraulically Placed Clay    Shale. M. Sc. Thesis, Dept. Civil Engineering, University of    Alberta, 257 p.-   Mimura, D. W. and Lord, E. R., 1991. Oil Sand Fine Tails Absorption    into Overburden Clay Shales—A Dry Landscape Alternative. Petroleum    Society of CIM and AOSTRA, Paper No. 91-128, 10 p.-   Morgenstern, N. R. and Scott, D. J., 1997. Oil Sand Geotechnique.    Geotechnical News, Special 1997, Pages 102-109.-   Terzaghi, K., Peck, R. B. and G. Mesri, 1996. Soil Mechanics in    Engineering Practice, 3rd Edition, John Wiley & Sons, Inc., New    York.

We claim:
 1. A process for enhancing the solidification of tailingscomprising: a) providing overburden having a moisture content rangingfrom about 15 wt % to about 25 wt % and comminuting the overburden toform comminuted overburden; b) providing tailings having a solidscontent ranging from about 1 wt % to about 70 wt %; c) combining thetailings with the comminuted overburden at a tailings:overburden ratioranging from about 0.2:1.0 (bulk volume) to about 0.4:1.0 (bulk volume)to form treated overburden; and d) depositing the treated overburden toproduce a substantially solidified deposit.
 2. The process of claim 1,wherein the tailings are added to the overburden at atailings:overburden ratio of about 0.2:1.0 (bulk volume).
 3. The processof claim 1, wherein in step (a), the comminuted overburden has a lumpsize of about 600 mm or less.
 4. The process of claim 1, wherein thedeposit has an undrained shear strength greater than the undrained shearstrength of the tailings alone.
 5. The process of claim 4, wherein thedeposit has an undrained shear strength greater than about 5 kPa.
 6. Theprocess of claim 1, wherein the deposit has a solids content of at leastabout 70 wt %.
 7. The process of claim 1, further comprising compactingthe treated overburden prior to depositing the treated overburden toproduce the substantially solidified deposit.
 8. The process of claim 1,further comprising disposing the deposit in an area using a dry stackingmode of disposal, or dewatering the deposit by consolidation, dryingand/or desiccation using 1 to 2 meter lifts, or greater than 2 meterlifts.
 9. The process of claim 1, further comprising disposing thedeposit in layers to alternate with layers of compacted lifts.
 10. Theprocess of claim 9, wherein the compacted lifts comprise sand.
 11. Theprocess of claim 1, wherein the tailings are oil sands fluid finetailings.
 12. The process of claim 1, wherein the tailings are treatedwith an additive selected from a coagulant or a flocculant prior toaddition to the overburden.
 13. The process as claimed in claim 1,wherein the tailings are oil sands fluid fine tailings that have beensubjected to centrifugation to form a centrifuge cake.
 14. The processas claimed in claim 13, whereby an initial mass strength of thesubstantially solidified deposit is about 25 to about 50 kPa.
 15. Theprocess as claimed in claim 1, wherein the tailings have a solidscontent ranging from about 10 wt % to about 60 wt %.
 16. The process asclaimed in 13, wherein the oil sand fluid fine tailings are treated withan additive selected from a coagulant or a flocculant or both prior tocentrifugation.